Method for identifying touch object

ABSTRACT

A method for identifying touch object has steps of presetting a range of slopes for noise signals, identifying multiple sensed signals, each having a slope higher than the range of slopes for noise signals in a sensing frame, and if the slope of each sensed signal is higher than an upper bound of the range of slopes for noise signals and is higher than each of those of the adjacent sensed signals, determining that the sensed signal is sensed from a corresponding sensed point touched by a stylus. Accordingly, the method can correctly identify a range touched by a stylus from the sensed signals combined with LCM noise signals.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for identifying a stylus on a touch panel and more particularly to a method for distinguishing correct sensed signals of touch objects on a touch panel from noises.

2. Description of the Related Art

When a touch panel is mounted on a liquid crystal module (LCM), noises are generated because of the scanning of the scan lines on the LCM and the noises are hereinafter called LCM noises impacting on positional precision of the touch panel in determining touched points on the touch panel. With reference to FIGS. 5A and 5C, capacitance variation values, dV_(stylus) and dV_(finger) are equal to a base value subtracted by the capacitance values of true respective sensed signals of a stylus and a finger therefrom, respectively correspond to control ranges for sensing a stylus and fingers on a touch panel, and increase as a result of the LCM noises. If the capacitance variation values, dV_(stylus) and dV_(finger) need to be correctly calculated, the capacitance variation values caused by the corresponding LCM noises must be deducted therefrom. To tackle the LCM noises, regular approaches preset a fixed noise threshold value and directly deducts the noise threshold value from the capacitance variation values of the sensed signals of stylus or finger so as to avoid the influence of the LCM noises.

However, with reference to FIG. 5B, as the true capacitance variation value of the LCM noise dVR_(noise) is not a constant, it's difficult to decide a fixed noise threshold value. If the noise threshold value is preset to be a relatively low constant, due to the fluctuating dVR_(noise), it is easy for a sensed signal to be incorrectly identified as that of a stylus. On the contrary, true touched points of the stylus may be ignored. Since dV_(finger) is normally greater than dV_(stylus) and dV_(noise), the sensed signals for fingers are not easy to be incorrectly identified as those for other touch objects.

Sensing a stylus or fingers touching on a touch panel is commonplace nowadays. How to correctly identify the position touched by the stylus from the sensed signals combined with the LCM noises is definitely the name of the game.

SUMMARY OF THE INVENTION

An objective of the present invention is to provide a method for identifying touch object, which is capable of correctly identifying positions on a touch panel touched by a stylus and being immune to the influence of the noises generated from the liquid crystal module (LCM).

To achieve the foregoing objective, the method for identifying touch object has steps of:

-   -   presetting a range of slopes for noise signals;     -   identifying multiple sensed signals, each having a slope higher         than the range of slopes for noise signals in a sensing frame;         and     -   if the slope of each sensed signal is higher than an upper bound         of the range of slopes for noise signals and is higher than each         of those of the adjacent sensed signals, determining that the         sensed signal is sensed from a corresponding sensed point         touched by a stylus.

As the slopes of the sensed signals of the stylus are noticeably higher than those of noises, the present invention employs a predetermined range of slopes for noise signals and compares it with the slopes of the sensed signals. The sensed signals having the slopes higher than those of the noises are picked up and the capacitance variation values thereof are compared with those of the adjacent sensed signals to determine if they are greater. If positive, the sensed signals having the higher slopes can be determined as the sensed signals generated by the stylus and the sensed points touched by the stylus can be further defined. Therefore, the method of the present invention can truly identify the positions touched by the stylus from the sensed signals combined with the LCM noise signals.

Other objectives, advantages and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a flow diagram of a first embodiment of a method for identifying touch object in accordance with the present invention;

FIG. 1B is a flow diagram of a second embodiment of a method for identifying touch object in accordance with the present invention;

FIG. 1C is a flow diagram of a base value updating step for the methods in FIGS. 1A and 1B;

FIG. 1D is schematic view of capacitance variation values corresponding to a stylus, a finger and noises on a sensing frame in accordance with the present invention;

FIG. 2A is a detailed flow diagram of the method in FIG. 1B;

FIG. 2B is a flow diagram of a continued portion of the method in FIG. 2A;

FIG. 2C is a flow diagram of a continued portion of the method in FIG. 2B;

FIG. 2D a flow diagram of a step for identifying coordinates of touched points by a stylus of the method in FIG. 2C;

FIGS. 3A to 3D are schematic views of four effective coordinates touched by the stylus and identified by the step in FIG. 2C;

FIGS. 4A to 4D are schematic views of four steps for calculating coordinates of positions touched by the stylus in FIG. 3A;

FIG. 5A is a schematic view of a sensing frame of a conventional touch panel;

FIG. 5B is a schematic view of capacitance variation values generated by noises on the sensing frame in FIG. 5A; and

FIG. 5C is a schematic view of capacitance variation values corresponding to points touched by a stylus and a finger and affected by the noises on the sensing frame in FIG. 5A.

DETAILED DESCRIPTION OF THE INVENTION

The present invention targets at correctly identifying positions touched by a stylus from sensed signals combined with the LCM noises. The approach of the present invention lies in that slopes of the ascending edges of curves for capacitance variation values of sensed signals of the stylus are noticeably higher than those of the ascending edges of a curve for capacitance variation values of noise signals. Furthermore, a range of slopes of the capacitance variation values for the noise signals is predetermined, and according to the range of slopes for the noise signals, the sensed signals having slopes higher than an upper bound of the range of slopes for the noise signals in a current sensing frame are identified and treated as non-LCM noises. If the slope of a sensed signal is higher than the upper bound of the range of slopes for the noise signals and the capacitance variation values of the sensed signal is higher than each of those of adjacent sensed signals, the sensed signal is considered as a sensed signal of a sensed point touched by the stylus. Detailed embodiments follow to describe implementation of the foregoing concepts.

The method for identifying touch object of the present invention may be applied to self-sensing sensing frames or full mutual-scanning sensing frames. As the self-sensing sensing frames include multiple sensing lines respectively generating sensed signals, the method for identifying touch object of the present invention acquires the capacitance variation values of sensed signals on each sensing line and determines the slopes of the sensed signals in accordance with the capacitance variation values. If the slope of a sensed signal is greater than an upper bound of the range of slopes for the noise signals and is greater than those of all the sensed signals, the point from which the sensed signal is sensed is a point touched by the stylus.

With reference to FIGS. 1A and 1C, a first embodiment of a method for identifying touch object in accordance with the present invention is applied to full-scanning sensing frames and has the following steps.

Preset a noise ripple range dVR_(noise) as a range of slopes for noise signals (S10).

Acquire a capacitance variation value of each sensed point in a sensing frame (S11). The capacitance variation value of each sensed point is equal to a value of subtracting a capacitance value of a corresponding true sensed signal from a base value and is positive.

Identify sensed points touched by the stylus from multiple sensed points of the sensing frame, obtain a difference value between the capacitance variation value of a sensed signal of each sensed point and that of an adjacent sensed point to define as a slope of the sensed signal, select each sensed point having the slope greater than an upper bound of the noise ripple range dVR_(noise), and compare the capacitance variation value of the selected sensed point with those of the adjacent sensed points, if the capacitance variation value of the selected sensed point is a maximum, determine the selected sensed point as a sensed point touched by the stylus (S12).

Determine if the current sensing frame has any sensed point touched by the stylus (S13). If negative, update the base value (S14) and resume (S11) after receiving next sensing frame. Otherwise, resume (S11) after receiving next sensing frame.

With reference to FIGS. 1B and 1D, a second embodiment of a method for identifying touch object in accordance with the present invention is applied to a touch panel capable of being touched by fingers and a stylus, and has the following steps.

Preset a noise ripple range dVR_(noise) as a range of slopes for noise signals and a capacitance variation threshold for finger dVf_(th) (S10′).

Acquire capacitance variation values of all sensed points in a sensing frame (S11′). The capacitance variation value of each sensed point is equal to a value of subtracting a capacitance value of a corresponding true sensed signal from a base value and is positive.

Obtain a difference value between the capacitance variation value of a sensed signal of each sensed point and that of an adjacent sensed point to define as a slope of the sensed signal, select the sensed point having the slope less than a lower bound of the noise ripple range dVR_(noise), compare the capacitance variation value of the sensed point with the capacitance variation threshold for finger dVf_(th), and If the capacitance variation value of the sensed point is greater than the dVf_(th), determine the sensed signal of the sensed point as a non-LCM noise (S12′)

Compare the capacitance variation value of each sensed point greater than an upper bound of the noise ripple range dVR_(noise) with those of the adjacent sensed points, and if the capacitance variation value of the sensed point is a maximum, determine the sensed point as a point touched by the stylus (S13′).

Determine if there is any non-LCM noise or sensed point touched by the stylus (S14′). If negative, update the base value (S15′) and resume (S11′) after receiving next sensing frame. Otherwise, resume (S11′) after receiving next sensing frame.

With reference to FIG. 1C, each step (S14, S15′) of updating the base value in the foregoing two embodiments has the following sub-steps.

Sequentially obtain the capacitance values and a minimum of the capacitance values of all sensed points on each column through all the columns of each sensing frame (S140).

Subtract the base value from the minimum value (S141).

Determine if the difference value is greater than zero (S142).

If positive, update the base value by adding the difference value to the base value for the row (S143).

Otherwise, keep the base value intact (S144).

As the base value for each row fluctuates after the touch panel is powered on, updating the base values can therefore enhance the precision of the present invention in terms of identification of points touched by the stylus.

With reference to FIGS. 2A to 2C, the step in FIG. 1C is further described in details as follows.

In the step S140, the sensing frame has multiple sensed points aligned in the form of a matrix with n rows and m columns. A buffer of each sensed point is stored with a preset value. In the present embodiment, the preset value is nonzero.

The buffers of the sensed points are sequentially stored column by column and row by row with zero, a difference value or a capacitance variation value respectively representing a code for LCM noise, a sensed signal of the stylus and a sensed signal of a finger. The physical implementation is as follows.

Acquire the capacitance variation values of all the sensed points on one of the rows and all columns crossed through the row in a row-by-row order (S300).

Subtract the capacitance variation value of the sensed point on the second column crossed by the row from that on the first column crossed by the row, and determine if the difference value is greater than the noise ripple range (S301).

If positive, store the difference value in the buffer of the sensed point on the first column crossed by the row because the sensed signal of the sensed point on the first column crossed by the row is determined to be a non-LCM noise (S302).

If negative, store zero in the buffer of the sensed point because the sensed signal of the sensed point on the first column crossed by the row is an LCM noise (S303).

Further sequentially group each three consecutive sensed points (a previous sensed point, a present sensed point and a next sensed point on the row to determine the following steps before storing the buffer of last column crossed by the row (S304).

(a) Determination of an LCM Noise

Respectively subtract the capacitance variation values of the previous sensed point and the next sensed point from the present sensed point, and determine if the two difference values are both less than the lower bound of the noise ripple range (S305). For example, if the present sensed point is the second sensed point on the row crossed by the second column, the previous sensed point will be a first sensed point and the next sensed point will be third sensed point. One of the difference values is calculated by subtracting the capacitance variation value of the first sensed point from that of the second sensed point, and the other one is calculated by subtracting the capacitance variation value of the third sensed point from that of the second sensed point.

If positive, store zeros in the buffers of the three sensed points (S306).

Otherwise, first determine if the buffer of the present sensed point contains the preset value (S307), which indicates that the sensed point has not been determined yet, and then perform the following steps.

(b) Determination of a Sensed Point Touched by a Finger

Determine if the capacitance variation value of the present sensed point is greater than the capacitance variation threshold for finger (S308).

If positive, store the current capacitance variation value in the buffer of the present sensed point because the present sensed point is determined to be a point touched by a finger (S309).

Otherwise, the present sensed point is determined to be a point touched by the stylus, and further determine the following steps.

(c) Determination of a Sensed Point Touched by the Stylus

Respectively subtract the capacitance variation values of the previous sensed point and the next sensed point from the present sensed point, select the smaller one of the two difference values and compare with zero to determine if the capacitance variation value of the present sensed point is greater than that of the previous or next sensed point (S310).

If the smaller difference value is greater than zero, store the smaller difference value in the buffer of the present sensed point because the present sensed point is determined to be a sensed point touched by the stylus (S311).

Otherwise, if the smaller difference value is less than zero, store zero in the buffer of the present sensed point because the sensed signal of the present sensed point is determined to be an LCM noise (S312).

Determine if all the sensed points on the present row crossed by the first column to a second to last column have been determined to be touched by the stylus (S313). Determination of the last sensed point on the row crossed by the last column is identical to the determination of the sensed points the row crossed by the first column.

Subtract the capacitance variation value of the sensed point on the row crossed by the second to last column from the capacitance variation value of the sensed point on the row crossed by the last column (S314).

Determine if the difference value is greater than the upper bound of the noise ripple range (S315).

If positive, store the difference value in the buffer of the sensed point on the row crossed by the last column because the sensed signal of the sensed point is determined to be a non-LCM noise (S316).

Otherwise, store zero in the buffer of the sensed point on the row crossed by the last column because the sensed signal of the sensed point is determined to be an LCM noise (S317).

Resume step S300 until the sensed points of on the last row crossed by all the columns are determined (S318).

To further precisely identify the sensed points touched by the stylus, with reference to FIG. 2D, the values stored in the buffer of each sensed point can be further determined by the following steps:

Preset an upper threshold and a lower threshold of capacitance variation for stylus (S319).

Compare the values stored in the buffers of all the sensed points on one of the rows with the lower threshold of capacitance variation for stylus in a row-by-row order to determine if the stored value of the sensed point on the row crossed by each column is greater than the lower threshold (S320).

If positive, determine if the capacitance variation value of the sensed point is greater than those of all the adjacent sensed points (S321).

If negative, determine the sensed point as a sensed point not touched by the stylus (S322).

If positive, determine if the capacitance variation value of the sensed point is less than the upper threshold of capacitance variation for stylus (S323).

If positive, determine the present sensed point as a true touched point of the stylus (S324).

If the present invention is applied to a multi-touch touch panel, there is a chance that multiple sensed points may be determined as the touched points of the stylus in the present steps. For such application, according to the specification of an applicable touch panel, for example, if five styluses are allowed in operation, multiple (5) buffers for stylus need to be prepared beforehand.

When identifying true sensed points touched by the styluses, first determine if any unoccupied buffer for stylus is available (S325).

If positive, store coordinates of the present sensed point in terms of column and row associated with the unoccupied buffer for stylus (S326).

If there is a sixth sensed point qualifying for the determination under the same specification, the capacitance variation value of the sixth sensed point is further compared with the minimal capacitance variation value of the five sensed points. If the capacitance variation value of the sixth sensed point is greater, the coordinates thereof are overwritten to the buffer for stylus having the least capacitance variation value (S327). Up to here, coordinates of sensed points for single stylus or multiple styluses can be identified.

However, coordinates of a stylus effective for the controller of a touch panel to use fail to be calculated by interpolation using coordinates of single sensed point. At least 2*2 sensed points arranged in a two-by-two array within the matrix of the sensing frame are required to calculate actual coordinates of positions touched by the stylus. With reference to FIGS. 3A to 3D, coordinates of a single sensed point whose capacitance variation value must be greater than that of the rest of three sensed points are identified through the methods and step in FIGS. 2A to 2D. Effective coordinates of the rest of three sensed points can be further identified, and there are four possibilities described as follows.

Suppose that the coordinates of column and row (I, J) of a single sensed point is the coordinates of (i, j) of a present sensed point, the capacitance variation values of the sensed points on the previous row (j−1) and next row (j+1) of the single sensed point are compared, and there are four possibilities as shown in FIGS. 3A to 3D. When the capacitance variation value of the previous row (j−1) is greater than that of the next row (j+1), the coordinate of row (J) for the sensed point on the upper left corner may map the coordinate of row for the sensed point on the upper left corner of the dotted 2*2 array as shown in FIG. 3A or 3D. Next, the capacitance variation values of the sensed points on the previous column (i−1) and next column (i+1) of the single sensed point are then compared to determine the coordinate of column for the single sensed point on the upper left corner of the dotted 2*2 array. The coordinate of column (I) for the sensed point on the upper left corner maps the coordinate of row for the sensed point on the upper left corner of the dotted 2*2 area as shown in FIG. 3A if the capacitance variation value of the previous column (i−1) is greater than that of the next column (i+1), or maps that as shown in FIG. 3D otherwise. Similarly, when the capacitance variation value of the previous row (j−1) is less than that of the next row (j+1), the coordinate of row (J) for the sensed point on the upper left corner may map the coordinate of row for the sensed point on the upper left corner of the dotted 2*2 array as shown in FIG. 3B or 3C. Next, the capacitance variation values of the sensed points on the previous column (i−1) and next column (i+1) of the single sensed point are then compared to determine the coordinate of column for the single sensed point on the upper left corner of the dotted 2*2 array. The coordinate of column (I) for the sensed point on the upper left corner maps the coordinate of row for the sensed point on the upper left corner of the dotted 2*2 area as shown in FIG. 3B if the capacitance variation value of the previous column (i−1) is greater than that of the next column (i+1), or maps that as shown in FIG. 3C otherwise. Once the coordinates (I, J) of the single sensed point on the upper left corner are determined, the coordinates of all the sensed points on the 2*2 array can be determined.

Moreover, to precisely calculate the coordinates touched by the stylus by interpolation, the values of LCM noise and vertical noise must be deducted from the capacitance variation values of the sensed points in the 2*2 array. With reference to FIGS. 4A to 4D, the sensed points in the 2*2 array determined in FIG. 3A and respectively having the capacitance variation values, dV11, dV12, dV21 and dV22, are shown. The minimum values of the capacitance variation values B11, B12 of the sensed points on the previous adjacent row j−2 and the next adjacent row j+1 on the same column i−1 are respectively deducted from the original capacitance variation values, dV11 and dV12, and the maximum values of zero and the difference values are respectively taken to obtain first capacitance variation values W11 and W12 as shown in Eqns 1 and 2 Similarly, first capacitance variation values W21 and W22 can be obtained by respectively deducting the minimum values B21, B22 of the capacitance variation values of the sensed points on the previous adjacent row j−2 and the next adjacent row j+1 on the same column i from the original capacitance variation values, dV21 and dV22, and respectively taking the maximum values of zero and the difference values as shown in Eqns 3 and 4. Next, the capacitance variation values of the sensed points A11 and A12 on the rows j−1 and j and the column i−2 respectively minus the capacitance variation values of another two adjacent sensed points A10 and A13 on the same column to obtain respective capacitance variation difference values A11′ and A12′. Similarly, the capacitance variation values of the sensed points A21 and A22 on the rows j−1 and j and the column i+1 respectively minus the capacitance variation values of another two adjacent sensed points A20 and A23 on the same column to obtain capacitance variation difference values A21′ and A22′. Thus, the LCM noises can be deducted from the capacitance variation difference values A11′, A12′, A21′ and A22′. The minimum value of the capacitance variation difference values A11′ and A21′ on the row j−1 and the columns i−2 and i+1 is deducted from the first capacitance variation values, W11 and W21, on the columns i−1 and i and the row j−1, and the maximum of zero and each difference value is taken to obtain a corresponding actual capacitance variation value W11′ and W21′ on the columns i−1 and i and the row j−1 as shown in Eqns 5 and 7. Similarly, actual capacitance variation value W12′ and W22′ on the columns i−1 and i and the row j can be obtained by deducting the minimum value of the capacitance variation difference values A12′ and A22′ on the same row from the first capacitance variation values, W12 and W22, on the columns i−1 and i and the row j and taking the maximum value of zero and each difference value as shown in Eqns 6 and 8. The actual capacitance variation values W11′, W12′, W21′ and W22′ are employed to calculate the effective coordinates of a sensed point touched by the stylus by interpolation.

W11=max(0,dV11−min(B11,B12)))  (1)

W12=max(0,dV12−min(B11,B12)))  (2)

W21=max(0,dV21−min(B21,B22)))  (3)

W22=max(0,dV22−min(B21,B22)))  (4)

W11′=max(0,W11−min(A11′,A21′)))  (5)

W12′=max(0,W12−min(A12′,A22′)))  (6)

W21′=max(0,W21−min(A11′,A21′)))  (7)

W22′=max(0,W22−min(A12′,A22′)))  (8)

As the slopes of the capacitance variation values of the sensed points within a touch range for fingers and the stylus are relatively high, the present invention respectively determines the difference values between the capacitance variation values of relevant sensed points within the touch range, defines the difference values as the slopes, and compares with the noise ripple range. If the slopes fall in the noise ripple range, the sensed points are determined to be caused by noises. Otherwise, the sensed points may be touched by a finger or a stylus. Furthermore, the capacitance variation value of the sensed point is compared with those of adjacent sensed points to determine if it is a maximum. If positive, the sensed point can then be determined to be touched by a stylus instead of a finger. Accordingly, the method of the present invention can truly eliminate the LCM noises and correctly identify actual sensed points touched by the stylus.

Even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only. Changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed. 

What is claimed is:
 1. A method for identifying touch object comprising: presetting a range of slopes for noise signals; identifying multiple sensed signals, each having a slope higher than the range of slopes for noise signals in a sensing frame; and if the slope of each sensed signal is higher than an upper bound of the range of slopes for noise signals and is higher than each of those of the adjacent sensed signals, determining that the sensed signal is sensed from a corresponding sensed point touched by a stylus.
 2. The method as claimed in claim 1, wherein the step of identifying sensed signals comprises steps of: presetting a noise ripple range as the range of slopes for noise signals; acquiring a capacitance variation value of the sensed signal of each sensed point in the sensing frame and determining the slope of the sensed signal according to the capacitance variation value; and if the capacitance variation value is greater than the slopes of the noise ripple range and is a maximum among the capacitance variation values of the sensed signals among all the sensed points in the sensing frame, determining that the sensed point is touched by the stylus.
 3. The method as claimed in claim 1, wherein the step of identifying sensed signals comprises steps of: presetting a noise ripple range as the range of slopes for noise signals; acquiring a capacitance variation value of the sensed signal of each sensed point in the sensing frame; and identifying the sensed points touched by the stylus from multiple sensed points of the sensing frame by obtaining a difference value between the capacitance variation value of a sensed signal of each sensed point and that of an adjacent sensed point to define as a slope of the sensed signal, selecting each sensed point having the slope greater than the upper bound of the noise ripple range, comparing the capacitance variation value of the selected sensed point with those of the adjacent sensed points, and if the capacitance variation of the selected sensed point is a maximum, determining that the selected sensed point is a sensed point touched by the stylus.
 4. The method as claimed in claim 1, wherein the step of identifying sensed signals comprises steps of: presetting a noise ripple range as the range of slopes for noise signals and a capacitance variation threshold for finger; acquiring a capacitance variation value of the sensed signal of each sensed point in the sensing frame; and obtaining a difference value between the capacitance variation value of a sensed signal of each sensed point and that of an adjacent sensed point to define as a slope of the sensed signal, selecting the sensed point having the slope less than a lower bound of the noise ripple range, comparing the capacitance variation value of the selected sensed point with the capacitance variation threshold for finger, and if the capacitance variation of the sensed point is greater than the capacitance variation threshold for finger, determining that the sensed signal of the sensed point is a non-LCM noise; comparing the capacitance variation value of each sensed point greater than an upper bound of the noise ripple range with those of the adjacent sensed points, and if the capacitance variation value of the sensed point is a maximum, determining that the sensed point is touched by the stylus.
 5. The method as claimed in claim 3, wherein the capacitance variation value of each sensed point is equal to a value subtracting a capacitance value of a corresponding true sensed signal from a base value; and after the step of determining that the selected sensed point is a sensed point touched by the stylus, the method further comprises a step of updating the base value performed when determining that the current sensing frame has no sensed points touched by the stylus.
 6. The method as claimed in claim 4, wherein the capacitance variation value of each sensed point is equal to a value subtracting a capacitance value of a corresponding true sensed signal from a base value; and after the step of determining that the selected sensed point is a sensed point touched by the stylus, the method further comprises a step of updating the base value performed when determining that the current sensing frame has no non-LCM noise or sensed point touched by the stylus.
 7. The method as claimed in claim 5, wherein the step of updating the base value has steps of: sequentially obtaining the capacitance values and a minimum of the capacitance values of all sensed points on each column through all the columns of each sensing frame; subtracting the minimum value from the base value; determining if the difference value is greater than zero; if positive, updating the base value by adding the difference value to the base value for the row; and if negative, keeping the base value intact.
 8. The method as claimed in claim 6, wherein the step of updating the base value has steps of: sequentially obtaining the capacitance values and a minimum of the capacitance values of all sensed points on each row and all the columns of each sensing frame; subtracting the minimum value from the base value; determining if the difference value is greater than zero; if positive, updating the base value by adding the difference value to the base value for the row; and if negative, keeping the base value intact.
 9. The method as claimed in claim 4, wherein in the step of determining the non-LCM noise or sensed point touched by the stylus, each sensing frame has multiple sensed points aligned in the form of a matrix with multiple rows and multiple columns, each sensed point has a buffer stored with a preset value, and the step of determining the non-LCM noise or sensed point touched by the stylus further has steps of: acquiring the capacitance variation values of all the sensed points on one of the rows and all columns crossed through the row in a row-by-row order; subtracting the capacitance variation value of the sensed point on the second column crossed by the row from that on the sensed point on the first column crossed by the row, and determining if the difference value is greater than the upper bound of the noise ripple range; if negative, storing zero in the buffer of the sensed point to indicate that the sensed signal of the sensed point on the first column crossed by the row is an LCM noise; and if positive, storing the difference value in the buffer of the sensed point to indicate that the sensed signal of the sensed point on the first column crossed by the row is a non-LCM noise and further determining the following steps; sequentially grouping each three consecutive sensed points, a previous, a present and a next sensed point, on the row to perform the following steps before storing the buffer of last column of the row; (a) step of determining an LCM noise by: respectively subtracting the capacitance variation values of the previous sensed point and the next sensed point from the present sensed point; determining if the two difference values are both less than the lower bound of the noise ripple range; if positive, storing zeros in the buffers of the three sensed points to indicate that the sensed signals of the sensed points are LCM noise; and if negative, determining if the buffer of the present sensed point is the preset value and then performing the following steps; (b) step of determining a sensed point touched by a finger by: determining if the capacitance variation value of the present sensed point is greater than the capacitance variation threshold for finger; if positive, storing the current capacitance variation value in the present sensed point to indicate that the present sensed point is a point touched by a finger; and if negative, further determining the following steps; (c) step of determining a sensed point touched by the stylus by: respectively subtracting the capacitance variation values of the previous sensed point and the next sensed point from the capacitance variation values of the present sensed point; selecting the smaller one of the two difference values to compare with zero; if the smaller difference value is greater than zero, storing the smaller difference value in the buffer of the present sensed point; if the smaller difference value is less than zero, storing zero in the buffer of the present sensed point to indicate that the sensed signal of the present sensed point is an LCM noise; determining the sensed point on the last column crossed by the row by subtracting the capacitance variation value of the sensed point on the second to last column crossed by the row from the capacitance variation value of the sensed point on the last column crossed by the row, determining if the difference value is greater than the upper bound of the noise ripple range, if positive, storing the difference value in the buffer of the sensed point on the last column crossed by the row to indicate that the sensed signal of the sensed point is a non-LCM noise, and if negative, storing zero in the buffer of the sensed point on the last column crossed by the row to indicate that the sensed signal of the sensed point is an LCM noise; and resuming step of sequentially obtaining the capacitance values and a minimum until the sensed points of the last row crossed by all the columns are determined.
 10. The method as claimed in claim 6, wherein in the step of determining the non-LCM noise or sensed point touched by the stylus, each sensing frame has multiple sensed points aligned in the form of a matrix with multiple rows and multiple columns, each sensed point has a buffer stored with a preset value, and the step of determining the non-LCM noise or sensed point touched by the stylus further has steps of: acquiring the capacitance variation values of all the sensed points on one of the rows and all columns crossed through the row in a row-by-row order; subtracting the capacitance variation value of the sensed point on the second column crossed by the row from that on the sensed point on the first column crossed by the row, and determining if the difference value is greater than the upper bound of the noise ripple range; if negative, storing zero in the buffer of the sensed point to indicate that the sensed signal of the sensed point on the first column crossed by the row is an LCM noise; and if positive, storing the difference value in the buffer of the sensed point to indicate that the sensed signal of the sensed point on the first column crossed by the row is a non-LCM noise and further determining the following steps; sequentially grouping each three consecutive sensed points, a previous, a present and a next sensed point, on the row to perform the following steps before storing the buffer of last column of the row; (a) step of determining an LCM noise by: respectively subtracting the capacitance variation values of the previous sensed point and the next sensed point from the present sensed point; determining if the two difference values are both less than the lower bound of the noise ripple range; if positive, storing zeros in the buffers of the three sensed points to indicate that the sensed signals of the sensed points are LCM noise; and if negative, determining if the buffer of the present sensed point is the preset value and then performing the following steps; (b) step of determining a sensed point touched by a finger by: determining if the capacitance variation value of the present sensed point is greater than the capacitance variation threshold for finger; if positive, storing the current capacitance variation value in the present sensed point to indicate that the present sensed point is a point touched by a finger; and if negative, further determining the following steps; (c) step of determining a sensed point touched by the stylus by: respectively subtracting the capacitance variation values of the previous sensed point and the next sensed point from the present sensed point; selecting the smaller one of the two difference values to compare with zero; if the smaller difference value is greater than zero, storing the smaller difference value in the present sensed point; if the smaller difference value is less than zero, storing zero in the buffer of the present sensed point to indicate that the sensed signal of the present sensed point is an LCM noise; determining the sensed point on the last column crossed by the row by subtracting the capacitance variation value of the sensed point on the second two last column crossed by the row from the capacitance variation value of the sensed point on the last column crossed by the row, determining if the difference value is greater than the upper bound of the noise ripple range, if positive, storing the difference value in the buffer of the sensed point on the last column crossed by the row to indicate that the sensed signal of the sensed point is a non-LCM noise, and if negative, storing zero in the buffer of the sensed point on the last column crossed by the row to indicate that the sensed signal of the sensed point is an LCM noise; and resuming step of sequentially obtaining the capacitance values and a minimum until the sensed points of the last row crossed by all the columns are determined.
 11. The method as claimed in claim 9, wherein the step of determining a sensed point touched by the stylus further has the following steps of: presetting an upper threshold and a lower threshold of capacitance variation for stylus; sequentially comparing the values stored in the buffer of all the sensed points on each row and all the columns with the lower threshold of capacitance variation for stylus in a column-by-column order and then a row-by-row order to determine if the stored value of the sensed point on each column crossed by the row is greater than the lower threshold; if positive, determining if the capacitance variation value of the sensed point is greater than those of all adjacent sensed points; if positive, determining if the capacitance variation value of the sensed point is less than the upper threshold of capacitance variation for stylus; and if positive, determining that the present sensed point is a sensed point touched by the stylus.
 12. The method as claimed in claim 10, wherein the step of determining a sensed point touched by the stylus further has the following steps of: presetting an upper threshold and a lower threshold of capacitance variation for stylus; sequentially comparing the values stored in the buffer of all the sensed points on each row and all the columns with the lower threshold of capacitance variation for stylus in a column-by-column order and then a row-by-row order to determine if the stored value of the sensed point on each column crossed by the row is greater than the lower threshold; if positive, determining if the capacitance variation value of the sensed point is greater than those of all adjacent sensed points; if positive, determining if the capacitance variation value of the sensed point is less than the upper threshold of capacitance variation for stylus; and if positive, determining that the present sensed point is a sensed point touched by the stylus.
 13. The method as claimed in claim 11, wherein after determining that the present sensed point is a sensed point touched by the stylus, coordinates containing the column and the row at which the present sensed point is located are stored in the buffer of the present sensed point.
 14. The method as claimed in claim 12, wherein after determining that the present sensed point is a sensed point touched by the stylus, coordinates containing the column and the row at which the present sensed point is located are stored in the buffer of the present sensed point.
 15. The method as claimed in claim 13, wherein when determining the sensed points touched by the styluses and storing the coordinates in a corresponding buffer, first determine if any unoccupied buffer for stylus is available; if negative, compare the capacitance variation value of the present sensed point with a minimal value of the capacitance variation values stored in the buffers of the rest of sensed points; if the capacitance variation value of the present sensed point is greater, the coordinates thereof are overwritten to the buffer of the sensed point having the least capacitance variation value.
 16. The method as claimed in claim 14, wherein when determining the sensed points touched by the styluses and storing the coordinates in a corresponding buffer, first determine if any unoccupied buffer for stylus is available; if negative, compare the capacitance variation value of the present sensed point with a minimal value of the capacitance variation values stored in the buffers of the rest of sensed points; if the capacitance variation value of the present sensed point is greater, the coordinates thereof are overwritten to the buffer of the sensed point having the least capacitance variation value.
 17. The method as claimed in claim 11, further comprising the following steps after the step of determining that the present sensed point is a sensed point touched by the stylus: determining a sensing point on an upper left corner of a two-by-two array within the matrix by selecting the coordinates of the sensed point touched by the stylus as a present sensed point; acquiring the capacitance variation values of the sensed points on two of the columns next to the present sensed point and determining a column of the coordinates of the sensed point on the upper left corner according to the capacitance variation values of the sensed points on the two columns next to the present sensed point; selecting the coordinates of the sensed point touched by the stylus as a present sensed point; acquiring the capacitance variation values of the sensed points on two of the rows next to the present sensed point and determining a row of the coordinates of the sensed point on the upper left corner according to the capacitance variation values of the sensed points on the two rows next to the present sensed point; and determining the two-by-two array of sensed points using the sensed point on the upper left corner.
 18. The method as claimed in claim 12, further comprising the following steps after the step of determining that the present sensed point is a sensed point touched by the stylus: determining a sensing point on an upper left corner of a two-by-two array within the matrix by selecting the coordinates of the sensed point touched by the stylus as a present sensed point; acquiring the capacitance variation values of the sensed points on two of the columns next to the present sensed point and determining a column of the coordinates of the sensed point on the upper left corner according to the capacitance variation values of the sensed points on the two columns next to the present sensed point; selecting the coordinates of the sensed point touched by the stylus as a present sensed point; acquiring the capacitance variation values of the sensed points on two of the rows next to the present sensed point and determining a row of the coordinates of the sensed point on the upper left corner according to the capacitance variation values of the sensed points on the two rows next to the present sensed point; and determining the two-by-two array of sensed points using the sensed point on the upper left corner.
 19. The method as claimed in claim 17, wherein the capacitance variation values of the two-by-two array of sensed points are used to determine effective coordinates of a touch object, and the effective coordinates of the touch object are determined by steps of: deducting a minimum value of the original capacitance variation values of the sensed points respectively on two columns next to the two-by-two array of sensed points and on each row of the two-by-two array of sensed points from the original capacitance variation value of each sensed point in the two-by-two array and on the same row, and obtaining a greater value of zero and the difference value as a first capacitance variation value of the sensed point in the two-by-two array; deducting the original capacitance variation value of each sensed point on both one of the rows and one of the columns next to the two-by-two array of sensed points from the original capacitance variation value of the sensed point on the same row and on adjacent one of the columns of the two-by-two array to obtain a capacitance variation difference value of the sensed point on the same row and on the adjacent column of the two-by-two array; deducting a minimum value of the two capacitance variation difference values of the sensed points respectively on the two rows next to the two-by-two array and on each column of the two-by-two array from the first capacitance variation value of each sensed point on the same column of the two-by-two array, and obtaining a greater value of zero and the difference value as an actual capacitance variation value of the sensed point in the two-by-two array; and using the actual capacitance variation values of the four sensing points in the two-by-two array to calculate the effective coordinates of the touch object by interpolation.
 20. The method as claimed in claim 18, wherein the capacitance variation values of the two-by-two array of sensed points are used to determine effective coordinates of a touch object, and the effective coordinates of the touch object are determined by steps of: deducting a minimum value of the original capacitance variation values of the sensed points respectively on two columns next to the two-by-two array of sensed points and on each row of the two-by-two array of sensed points from the original capacitance variation value of each sensed point in the two-by-two array and on the same row, and obtaining a greater value of zero and the difference value as a first capacitance variation value of the sensed point in the two-by-two array; deducting the original capacitance variation value of each sensed point on both one of the rows and one of the columns next to the two-by-two array of sensed points from the original capacitance variation value of the sensed point on the same row and on adjacent one of the columns of the two-by-two array to obtain a capacitance variation difference value of the sensed point on the same row and on the adjacent column of the two-by-two array; deducting a minimum value of the two capacitance variation difference values of the sensed points respectively on the two rows next to the two-by-two array and on each column of the two-by-two array from the first capacitance variation value of each sensed point on the same column of the two-by-two array, and obtaining a greater value of zero and the difference value as an actual capacitance variation value of the sensed point in the two-by-two array; and using the actual capacitance variation values of the four sensing points in the two-by-two array to calculate the effective coordinates of the touch object by interpolation.
 21. The method as claimed in claim 13, further comprising the following steps after the step of determining that the present sensed point is a sensed point touched by the stylus: determining a sensing point on an upper left corner of a two-by-two array within the matrix by selecting the coordinates of the sensed point touched by the stylus as a present sensed point; acquiring the capacitance variation values of the sensed points on two of the columns next to the present sensed point and determining a column of the coordinates of the sensed point on the upper left corner according to the capacitance variation values of the sensed points on the two columns next to the present sensed point; selecting the coordinates of the sensed point touched by the stylus as a present sensed point; acquiring the capacitance variation values of the sensed points on two of the rows next to the present sensed point and determining a row of the coordinates of the sensed point on the upper left corner according to the capacitance variation values of the sensed points on the two rows next to the present sensed point; and determining the two-by-two array of sensed points using the sensed point on the upper left corner.
 22. The method as claimed in claim 14, further comprising the following steps after the step of determining that the present sensed point is a sensed point touched by the stylus: determining a sensing point on an upper left corner of a two-by-two array within the matrix by selecting the coordinates of the sensed point touched by the stylus as a present sensed point; acquiring the capacitance variation values of the sensed points on two of the columns next to the present sensed point and determining a column of the coordinates of the sensed point on the upper left corner according to the capacitance variation values of the sensed points on the two columns next to the present sensed point; selecting the coordinates of the sensed point touched by the stylus as a present sensed point; acquiring the capacitance variation values of the sensed points on two of the rows next to the present sensed point and determining a row of the coordinates of the sensed point on the upper left corner according to the capacitance variation values of the sensed points on the two rows next to the present sensed point; and determining the two-by-two array of sensed points using the sensed point on the upper left corner.
 23. The method as claimed in claim 21, wherein the capacitance variation values of the two-by-two array of sensed points are used to determine effective coordinates of a touch object, and the effective coordinates of the touch object are determined by steps of: deducting a minimum value of the original capacitance variation values of the sensed points respectively on two columns next to the two-by-two array of sensed points and on each row of the two-by-two array of sensed points from the original capacitance variation value of each sensed point in the two-by-two array and on the same row, and obtaining a greater value of zero and the difference value as a first capacitance variation value of the sensed point in the two-by-two array; deducting the original capacitance variation value of each sensed point on both one of the rows and one of the columns next to the two-by-two array of sensed points from the original capacitance variation value of the sensed point on the same row and on adjacent one of the columns of the two-by-two array to obtain a capacitance variation difference value of the sensed point on the same row and on the adjacent column of the two-by-two array; deducting a minimum value of the two capacitance variation difference values of the sensed points respectively on the two rows next to the two-by-two array and on each column of the two-by-two array from the first capacitance variation value of each sensed point on the same column of the two-by-two array, and obtaining a greater value of zero and the difference value as an actual capacitance variation value of the sensed point in the two-by-two array; and using the actual capacitance variation values of the four sensing points in the two-by-two array to calculate the effective coordinates of the touch object by interpolation.
 24. The method as claimed in claim 22, wherein the capacitance variation values of the two-by-two array of sensed points are used to determine effective coordinates of a touch object, and the effective coordinates of the touch object are determined by steps of: deducting a minimum value of the original capacitance variation values of the sensed points respectively on two columns next to the two-by-two array of sensed points and on each row of the two-by-two array of sensed points from the original capacitance variation value of each sensed point in the two-by-two array and on the same row, and obtaining a greater value of zero and the difference value as a first capacitance variation value of the sensed point in the two-by-two array; deducting the original capacitance variation value of each sensed point on both one of the rows and one of the columns next to the two-by-two array of sensed points from the original capacitance variation value of the sensed point on the same row and on adjacent one of the columns of the two-by-two array to obtain a capacitance variation difference value of the sensed point on the same row and on the adjacent column of the two-by-two array; deducting a minimum value of the two capacitance variation difference values of the sensed points respectively on the two rows next to the two-by-two array and on each column of the two-by-two array from the first capacitance variation value of each sensed point on the same column of the two-by-two array, and obtaining a greater value of zero and the difference value as an actual capacitance variation value of the sensed point in the two-by-two array; and using the actual capacitance variation values of the four sensing points in the two-by-two array to calculate the effective coordinates of the touch object by interpolation.
 25. The method as claimed in claim 15, further comprising the following steps after the step of determining that the present sensed point is a sensed point touched by the stylus: determining a sensing point on an upper left corner of a two-by-two array within the matrix by selecting the coordinates of the sensed point touched by the stylus as a present sensed point; acquiring the capacitance variation values of the sensed points on two of the columns next to the present sensed point and determining a column of the coordinates of the sensed point on the upper left corner according to the capacitance variation values of the sensed points on the two columns next to the present sensed point; selecting the coordinates of the sensed point touched by the stylus as a present sensed point; acquiring the capacitance variation values of the sensed points on two of the rows next to the present sensed point and determining a row of the coordinates of the sensed point on the upper left corner according to the capacitance variation values of the sensed points on the two rows next to the present sensed point; and determining the two-by-two array of sensed points using the sensed point on the upper left corner.
 26. The method as claimed in claim 16, further comprising the following steps after the step of determining that the present sensed point is a sensed point touched by the stylus: determining a sensing point on an upper left corner of a two-by-two array within the matrix by selecting the coordinates of the sensed point touched by the stylus as a present sensed point; acquiring the capacitance variation values of the sensed points on two of the columns next to the present sensed point and determining a column of the coordinates of the sensed point on the upper left corner according to the capacitance variation values of the sensed points on the two columns next to the present sensed point; selecting the coordinates of the sensed point touched by the stylus as a present sensed point; acquiring the capacitance variation values of the sensed points on two of the rows next to the present sensed point and determining a row of the coordinates of the sensed point on the upper left corner according to the capacitance variation values of the sensed points on the two rows next to the present sensed point; and determining the two-by-two array of sensed points using the sensed point on the upper left corner.
 27. The method as claimed in claim 25, wherein the capacitance variation values of the two-by-two array of sensed points are used to determine effective coordinates of a touch object, and the effective coordinates of the touch object are determined by steps of: deducting a minimum value of the original capacitance variation values of the sensed points respectively on two columns next to the two-by-two array of sensed points and on each row of the two-by-two array of sensed points from the original capacitance variation value of each sensed point in the two-by-two array and on the same row, and obtaining a greater value of zero and the difference value as a first capacitance variation value of the sensed point in the two-by-two array; deducting the original capacitance variation value of each sensed point on both one of the rows and one of the columns next to the two-by-two array of sensed points from the original capacitance variation value of the sensed point on the same row and on adjacent one of the columns of the two-by-two array to obtain a capacitance variation difference value of the sensed point on the same row and on the adjacent column of the two-by-two array; deducting a minimum value of the two capacitance variation difference values of the sensed points respectively on the two rows next to the two-by-two array and on each column of the two-by-two array from the first capacitance variation value of each sensed point on the same column of the two-by-two array, and obtaining a greater value of zero and the difference value as an actual capacitance variation value of the sensed point in the two-by-two array; and using the actual capacitance variation values of the four sensing points in the two-by-two array to calculate the effective coordinates of the touch object by interpolation.
 28. The method as claimed in claim 26, wherein the capacitance variation values of the two-by-two array of sensed points are used to determine effective coordinates of a touch object, and the effective coordinates of the touch object are determined by steps of: deducting a minimum value of the original capacitance variation values of the sensed points respectively on two columns next to the two-by-two array of sensed points and on each row of the two-by-two array of sensed points from the original capacitance variation value of each sensed point in the two-by-two array and on the same row, and obtaining a greater value of zero and the difference value as a first capacitance variation value of the sensed point in the two-by-two array; deducting the original capacitance variation value of each sensed point on both one of the rows and one of the columns next to the two-by-two array of sensed points from the original capacitance variation value of the sensed point on the same row and on adjacent one of the columns of the two-by-two array to obtain a capacitance variation difference value of the sensed point on the same row and on the adjacent column of the two-by-two array; deducting a minimum value of the two capacitance variation difference values of the sensed points respectively on the two rows next to the two-by-two array and on each column of the two-by-two array from the first capacitance variation value of each sensed point on the same column of the two-by-two array, and obtaining a greater value of zero and the difference value as an actual capacitance variation value of the sensed point in the two-by-two array; and using the actual capacitance variation values of the four sensing points in the two-by-two array to calculate the effective coordinates of the touch object by interpolation.
 29. A method for identifying touch object comprising: presetting a range of slopes for noise signals; identifying multiple sensed signals, each having a slope higher than the range of slopes for noise signals in a sensing frame; and if the slope of each sensed signal is higher than an upper bound of the range of slopes for noise signals, determining the sensed signal as a non-LCM noise signal.
 30. The method as claimed in claim 29, wherein the step of identifying sensed signals comprises steps of: presetting a noise ripple range as the range of slopes for noise signals; acquiring a capacitance variation value of the sensed signal of each sensed point in the sensing frame and determining the slope of the sensed signal according to the capacitance variation value; and if the capacitance variation value is greater than the slopes of the noise ripple range, determining that a corresponding sensed signal is a non-LCM noise signal.
 31. The method as claimed in claim 29, wherein the step of identifying sensed signals comprises steps of: presetting a noise ripple range as the range of slopes for noise signals; acquiring a capacitance variation value of the sensed signal of each sensed point in the sensing frame; and identifying the sensed points touched by the stylus from multiple sensed points of the sensing frame by obtaining a difference value between the capacitance variation value of a sensed signal of each sensed point and that of an adjacent sensed point to define as a slope of the sensed signal, selecting each sensed point having the slope greater than the upper bound of the noise ripple range, comparing the capacitance variation value of the selected sensed point with those of the adjacent sensed points, and if the capacitance variation of the selected sensed point is a maximum, determining that the selected sensed point is a sensed point touched by the stylus.
 32. The method as claimed in claim 29, wherein the step of identifying sensed signals comprises steps of: presetting a noise ripple range as the range of slopes for noise signals and a capacitance variation threshold for finger; acquiring a capacitance variation value of the sensed signal of each sensed point in the sensing frame; obtaining a difference value between the capacitance variation value of a sensed signal of each sensed point and that of an adjacent sensed point to define as a slope of the sensed signal, selecting the sensed point having the slope less than a lower bound of the noise ripple range, comparing the capacitance variation value of the selected sensed point with the capacitance variation threshold for finger, and if the capacitance variation of the sensed point is greater than the capacitance variation threshold for finger, determining that the sensed signal of the sensed point is a non-LCM noise; and comparing the capacitance variation value of each sensed point greater than an upper bound of the noise ripple range with those of the adjacent sensed points, and if the capacitance variation value of the sensed point is a maximum, determining that the sensed point is touched by the stylus.
 33. The method as claimed in claim 31, wherein the capacitance variation value of each sensed point is equal to a value subtracting a capacitance value of a corresponding true sensed signal from a base value; and after the step of determining that the selected sensed point is a sensed point touched by the stylus, the method further comprises a step of updating the base value performed when determining that the current sensing frame has no sensed points touched by the stylus.
 34. The method as claimed in claim 32, wherein the capacitance variation value of each sensed point is equal to a value subtracting a capacitance value of a corresponding true sensed signal from a base value; and after the step of determining that the selected sensed point is a sensed point touched by the stylus, the method further comprises a step of updating the base value performed when determining that the current sensing frame has no non-LCM noise or sensed point touched by the stylus.
 35. The method as claimed in claim 33, wherein the step of updating the base value has steps of: sequentially obtaining the capacitance values and a minimum of the capacitance values of all sensed points on each row and all the columns of each sensing frame; subtracting the minimum value from the base value; determining if the difference value is greater than zero; if positive, updating the base value by adding the difference value to the base value for the row; and if negative, keeping the base value intact.
 36. The method as claimed in claim 34, wherein the step of updating the base value has steps of: sequentially obtaining the capacitance values and a minimum of the capacitance values of all sensed points on each row and all the columns of each sensing frame; subtracting the minimum value from the base value; determining if the difference value is greater than zero; if positive, updating the base value by adding the difference value to the base value for the row; and if negative, keeping the base value intact.
 37. The method as claimed in claim 32, wherein in the step of determining the non-LCM noise or sensed point touched by the stylus, each sensing frame has multiple sensed points aligned in the form of a matrix with multiple rows and multiple columns, each sensed point has a buffer stored with a preset value, and the step of determining the non-LCM noise or sensed point touched by the stylus further has steps of: acquire the capacitance variation values of all the sensed points on one of the rows and all columns crossed through the row in a row-by-row order; subtracting the capacitance variation value of the sensed point on the second column crossed by the row from that on the sensed point on the first column crossed by the row, and determining if the difference value is greater than the upper bound of the noise ripple range; if negative, storing in the buffer of the sensed point to indicate that the sensed signal of the sensed point on the first column crossed by the row is an LCM noise; and if positive, storing in the buffer of the sensed point to indicate that the sensed signal of the sensed point on the first column crossed by the row is a non-LCM noise and further determining the following steps; sequentially grouping each three consecutive sensed points, a previous, a present and a next sensed point, on the row to perform the following steps before storing the buffer of last column of the row; (a) step of determining an LCM noise by: respectively subtracting the capacitance variation values of the previous sensed point and the next sensed point from the present sensed point; determining if the two difference values are both less than the lower bound of the noise ripple range; if positive, storing in the buffers of the three sensed points to indicate that the sensed signals of the sensed points are LCM noise; and if negative, determining if the buffer of the present sensed point is the preset value and then performing the following steps; (b) step of determining a sensed point touched by a finger by: determining if the capacitance variation value of the present sensed point is greater than the capacitance variation threshold for finger; if positive, storing the current capacitance variation value in the present sensed point to indicate that the present sensed point is a point touched by a finger; and if negative, further determining the following steps; (c) step of determining a sensed point touched by the stylus by: respectively subtracting the capacitance variation values of the previous sensed point and the next sensed point from the present sensed point; selecting the smaller one of the two difference values to compare with zero; if the smaller difference value is greater than zero, storing the smaller difference value in the present sensed point; if the smaller difference value is less than zero, storing in the buffer of the present sensed point to indicate that the sensed signal of the present sensed point is an LCM noise; determining the sensed point on the last column crossed by the row by subtracting the capacitance variation value of the sensed point on the second two last column crossed by the row from the capacitance variation value of the sensed point on the last column crossed by the row, determining if the difference value is greater than the upper bound of the noise ripple range, if positive, storing the difference value in the buffer of the sensed point on the last column crossed by the row to indicate that the sensed signal of the sensed point is a non-LCM noise, and if negative, storing zero in the buffer of the sensed point on the last column crossed by the row to indicate that the sensed signal of the sensed point is an LCM noise; and resuming step of sequentially obtaining the capacitance values and a minimum until the sensed points of the last row crossed by all the columns are determined.
 38. The method as claimed in claim 34, wherein in the step of determining the non-LCM noise or sensed point touched by the stylus, each sensing frame has multiple sensed points aligned in the form of a matrix with multiple rows and multiple columns, each sensed point has a buffer stored with a preset value, and the step of determining the non-LCM noise or sensed point touched by the stylus further has steps of: acquiring the capacitance variation values of all the sensed points on one of the rows and all columns crossed through the row in a row-by-row order; subtracting the capacitance variation value of the sensed point on the second column crossed by the row from that on the sensed point on the first column crossed by the row, and determining if the difference value is greater than the upper bound of the noise ripple range; if negative, storing in the buffer of the sensed point to indicate that the sensed signal of the sensed point on the first column crossed by the row is an LCM noise; and if positive, storing in the buffer of the sensed point to indicate that the sensed signal of the sensed point on the first column crossed by the row is a non-LCM noise and further determining the following steps; sequentially grouping each three consecutive sensed points, a previous, a present and a next sensed point, on the row to perform the following steps before storing the buffer of last column of the row; (a) step of determining an LCM noise by: respectively subtracting the capacitance variation values of the previous sensed point and the next sensed point from the present sensed point; determining if the two difference values are both less than the lower bound of the noise ripple range; if positive, storing in the buffers of the three sensed points to indicate that the sensed signals of the sensed points are LCM noise; and if negative, determining if the buffer of the present sensed point is the preset value and then performing the following steps; (b) step of determining a sensed point touched by a finger by: determining if the capacitance variation value of the present sensed point is greater than the capacitance variation threshold for finger; if positive, storing the current capacitance variation value in the present sensed point to indicate that the present sensed point is a point touched by a finger; and if negative, further determining the following steps; (c) step of determining a sensed point touched by the stylus by: respectively subtracting the capacitance variation values of the previous sensed point and the next sensed point from the present sensed point; selecting the smaller one of the two difference values to compare with zero; if the smaller difference value is greater than zero, storing the smaller difference value in the present sensed point; if the smaller difference value is less than zero, storing in the buffer of the present sensed point to indicate that the sensed signal of the present sensed point is an LCM noise; determining the sensed point on the last column crossed by the row by subtracting the capacitance variation value of the sensed point on the second to last column crossed by the row from the capacitance variation value of the sensed point on the last column crossed by the row, determining if the difference value is greater than the upper bound of the noise ripple range, if positive, storing the difference value in the buffer of the sensed point on the last column crossed by the row to indicate that the sensed signal of the sensed point is a non-LCM noise, and if negative, storing zero in the buffer of the sensed point on the last column crossed by the row to indicate that the sensed signal of the sensed point is an LCM noise; and resuming step of sequentially obtaining the capacitance values and a minimum until the sensed points of the last row crossed by all the columns are determined.
 39. The method as claimed in claim 37, wherein the step of determining a sensed point touched by the stylus further has the following steps of: presetting an upper threshold and a lower threshold of capacitance variation for stylus; sequentially comparing the values stored in the buffer of all the sensed points on each row and all the columns with the lower threshold of capacitance variation for stylus in a column-by-column order and then a row-by-row order to determine if the stored value of the sensed point on each column crossed by the row is greater than the lower threshold; if positive, determining if the capacitance variation value of the sensed point is greater than those of all adjacent sensed points; if positive, determining if the capacitance variation value of the sensed point is less than the upper threshold of capacitance variation for stylus; and if positive, determining that the present sensed point is a sensed point touched by the stylus.
 40. The method as claimed in claim 38, wherein the step of determining a sensed point touched by the stylus further has the following steps of: presetting an upper threshold and a lower threshold of capacitance variation for stylus; sequentially comparing the values stored in the buffer of all the sensed points on each row and all the columns with the lower threshold of capacitance variation for stylus in a column-by-column order and then a row-by-row order to determine if the stored value of the sensed point on each column crossed by the row is greater than the lower threshold; if positive, determining if the capacitance variation value of the sensed point is greater than those of all adjacent sensed points; if positive, determining if the capacitance variation value of the sensed point is less than the upper threshold of capacitance variation for stylus; and if positive, determining that the present sensed point is a sensed point touched by the stylus.
 41. The method as claimed in claim 39, wherein after determining that the present sensed point is a sensed point touched by the stylus, coordinates containing the column and the row at which the present sensed point is located are stored in the buffer of the present sensed point.
 42. The method as claimed in claim 40, wherein after determining that the present sensed point is a sensed point touched by the stylus, coordinates containing the column and the row at which the present sensed point is located are stored in the buffer of the present sensed point.
 43. The method as claimed in claim 41, wherein when determining the sensed points touched by the styluses and storing the coordinates in a corresponding buffer, first determine if any unoccupied buffer for stylus is available; if negative, compare the capacitance variation value of the present sensed point with a minimal value of the capacitance variation values stored in the buffers of the rest of sensed points; if the capacitance variation value of the present sensed point is greater, the coordinates thereof are overwritten to the buffer of the sensed point having the least capacitance variation value.
 44. The method as claimed in claim 42, wherein when determining the sensed points touched by the styluses and storing the coordinates in a corresponding buffer, first determine if any unoccupied buffer for stylus is available; if negative, compare the capacitance variation value of the present sensed point with a minimal value of the capacitance variation values stored in the buffers of the rest of sensed points; if the capacitance variation value of the present sensed point is greater, the coordinates thereof are overwritten to the buffer of the sensed point having the least capacitance variation value.
 45. The method as claimed in claim 39, further comprising the following steps after the step of determining that the present sensed point is a sensed point touched by the stylus: determining a sensing point on an upper left corner of a two-by-two array within the matrix by selecting the coordinates of the sensed point touched by the stylus as a present sensed point; acquiring the capacitance variation values of the sensed points on two of the columns next to the present sensed point and determining a column of the coordinates of the sensed point on the upper left corner according to the capacitance variation values of the sensed points on the two columns next to the present sensed point; selecting the coordinates of the sensed point touched by the stylus as a present sensed point; acquiring the capacitance variation values of the sensed points on two of the rows next to the present sensed point and determining a row of the coordinates of the sensed point on the upper left corner according to the capacitance variation values of the sensed points on the two rows next to the present sensed point; and determining the two-by-two array of sensed points using the sensed point on the upper left corner.
 46. The method as claimed in claim 40, further comprising the following steps after the step of determining that the present sensed point is a sensed point touched by the stylus: determining a sensing point on an upper left corner of a two-by-two array within the matrix by selecting the coordinates of the sensed point touched by the stylus as a present sensed point; acquiring the capacitance variation values of the sensed points on two of the columns next to the present sensed point and determining a column of the coordinates of the sensed point on the upper left corner according to the capacitance variation values of the sensed points on the two columns next to the present sensed point; selecting the coordinates of the sensed point touched by the stylus as a present sensed point; acquiring the capacitance variation values of the sensed points on two of the rows next to the present sensed point and determining a row of the coordinates of the sensed point on the upper left corner according to the capacitance variation values of the sensed points on the two rows next to the present sensed point; and determining the two-by-two array of sensed points using the sensed point on the upper left corner.
 47. The method as claimed in claim 45, wherein the capacitance variation values of the two-by-two array of sensed points are used to determine effective coordinates of a touch object, and the effective coordinates of the touch object are determined by steps of: deducting a minimum value of the original capacitance variation values of the sensed points respectively on two columns next to the two-by-two array of sensed points and on each row of the two-by-two array of sensed points from the original capacitance variation value of each sensed point in the two-by-two array and on the same row, and obtaining a greater value of zero and the difference value as a first capacitance variation value of the sensed point in the two-by-two array; deducting the original capacitance variation value of each sensed point on both one of the rows and one of the columns next to the two-by-two array of sensed points from the original capacitance variation value of the sensed point on the same row and on adjacent one of the columns of the two-by-two array to obtain a capacitance variation difference value of the sensed point on the same row and on the adjacent column of the two-by-two array; deducting a minimum value of the two capacitance variation difference values of the sensed points respectively on the two rows next to the two-by-two array and on each column of the two-by-two array from the first capacitance variation value of each sensed point on the same column of the two-by-two array, and obtaining a greater value of zero and the difference value as an actual capacitance variation value of the sensed point in the two-by-two array; and using the actual capacitance variation values of the four sensing points in the two-by-two array to calculate the effective coordinates of the touch object by interpolation.
 48. The method as claimed in claim 46, wherein the capacitance variation values of the two-by-two array of sensed points are used to determine effective coordinates of a touch object, and the effective coordinates of the touch object are determined by steps of: deducting a minimum value of the original capacitance variation values of the sensed points respectively on two columns next to the two-by-two array of sensed points and on each row of the two-by-two array of sensed points from the original capacitance variation value of each sensed point in the two-by-two array and on the same row, and obtaining a greater value of zero and the difference value as a first capacitance variation value of the sensed point in the two-by-two array; deducting the original capacitance variation value of each sensed point on both one of the rows and one of the columns next to the two-by-two array of sensed points from the original capacitance variation value of the sensed point on the same row and on adjacent one of the columns of the two-by-two array to obtain a capacitance variation difference value of the sensed point on the same row and on the adjacent column of the two-by-two array; deducting a minimum value of the two capacitance variation difference values of the sensed points respectively on the two rows next to the two-by-two array and on each column of the two-by-two array from the first capacitance variation value of each sensed point on the same column of the two-by-two array, and obtaining a greater value of zero and the difference value as an actual capacitance variation value of the sensed point in the two-by-two array; and using the actual capacitance variation values of the four sensing points in the two-by-two array to calculate the effective coordinates of the touch object by interpolation.
 49. The method as claimed in claim 41, further comprising the following steps after the step of determining that the present sensed point is a sensed point touched by the stylus: determining a sensing point on an upper left corner of a two-by-two array within the matrix by selecting the coordinates of the sensed point touched by the stylus as a present sensed point; acquiring the capacitance variation values of the sensed points on two of the columns next to the present sensed point and determining a column of the coordinates of the sensed point on the upper left corner according to the capacitance variation values of the sensed points on the two columns next to the present sensed point; selecting the coordinates of the sensed point touched by the stylus as a present sensed point; acquiring the capacitance variation values of the sensed points on two of the rows next to the present sensed point and determining a row of the coordinates of the sensed point on the upper left corner according to the capacitance variation values of the sensed points on the two rows next to the present sensed point; and determining the two-by-two array of sensed points using the sensed point on the upper left corner.
 50. The method as claimed in claim 42, further comprising the following steps after the step of determining that the present sensed point is a sensed point touched by the stylus: determining a sensing point on an upper left corner of a two-by-two array within the matrix by selecting the coordinates of the sensed point touched by the stylus as a present sensed point; acquiring the capacitance variation values of the sensed points on two of the columns next to the present sensed point and determining a column of the coordinates of the sensed point on the upper left corner according to the capacitance variation values of the sensed points on the two columns next to the present sensed point; selecting the coordinates of the sensed point touched by the stylus as a present sensed point; acquiring the capacitance variation values of the sensed points on two of the rows next to the present sensed point and determining a row of the coordinates of the sensed point on the upper left corner according to the capacitance variation values of the sensed points on the two rows next to the present sensed point; and determining the two-by-two array of sensed points using the sensed point on the upper left corner.
 51. The method as claimed in claim 49, wherein the capacitance variation values of the two-by-two array of sensed points are used to determine effective coordinates of a touch object, and the effective coordinates of the touch object are determined by steps of: deducting a minimum value of the original capacitance variation values of the sensed points respectively on two columns next to the two-by-two array of sensed points and on each row of the two-by-two array of sensed points from the original capacitance variation value of each sensed point in the two-by-two array and on the same row, and obtaining a greater value of zero and the difference value as a first capacitance variation value of the sensed point in the two-by-two array; deducting the original capacitance variation value of each sensed point on both one of the rows and one of the columns next to the two-by-two array of sensed points from the original capacitance variation value of the sensed point on the same row and on adjacent one of the columns of the two-by-two array to obtain a capacitance variation difference value of the sensed point on the same row and on the adjacent column of the two-by-two array; deducting a minimum value of the two capacitance variation difference values of the sensed points respectively on the two rows next to the two-by-two array and on each column of the two-by-two array from the first capacitance variation value of each sensed point on the same column of the two-by-two array, and obtaining a greater value of zero and the difference value as an actual capacitance variation value of the sensed point in the two-by-two array; and using the actual capacitance variation values of the four sensing points in the two-by-two array to calculate the effective coordinates of the touch object by interpolation.
 52. The method as claimed in claim 50, wherein the capacitance variation values of the two-by-two array of sensed points are used to determine effective coordinates of a touch object, and the effective coordinates of the touch object are determined by steps of: deducting a minimum value of the original capacitance variation values of the sensed points respectively on two columns next to the two-by-two array of sensed points and on each row of the two-by-two array of sensed points from the original capacitance variation value of each sensed point in the two-by-two array and on the same row, and obtaining a greater value of zero and the difference value as a first capacitance variation value of the sensed point in the two-by-two array; deducting the original capacitance variation value of each sensed point on both one of the rows and one of the columns next to the two-by-two array of sensed points from the original capacitance variation value of the sensed point on the same row and on adjacent one of the columns of the two-by-two array to obtain a capacitance variation difference value of the sensed point on the same row and on the adjacent column of the two-by-two array; deducting a minimum value of the two capacitance variation difference values of the sensed points respectively on the two rows next to the two-by-two array and on each column of the two-by-two array from the first capacitance variation value of each sensed point on the same column of the two-by-two array, and obtaining a greater value of zero and the difference value as an actual capacitance variation value of the sensed point in the two-by-two array; and using the actual capacitance variation values of the four sensing points in the two-by-two array to calculate the effective coordinates of the touch object by interpolation.
 53. The method as claimed in claim 43, further comprising the following steps after the step of determining that the present sensed point is a sensed point touched by the stylus: determining a sensing point on an upper left corner of a two-by-two array within the matrix by selecting the coordinates of the sensed point touched by the stylus as a present sensed point; acquiring the capacitance variation values of the sensed points on two of the columns next to the present sensed point and determining a column of the coordinates of the sensed point on the upper left corner according to the capacitance variation values of the sensed points on the two columns next to the present sensed point; selecting the coordinates of the sensed point touched by the stylus as a present sensed point; acquiring the capacitance variation values of the sensed points on two of the rows next to the present sensed point and determining a row of the coordinates of the sensed point on the upper left corner according to the capacitance variation values of the sensed points on the two rows next to the present sensed point; and determining the two-by-two array of sensed points using the sensed point on the upper left corner.
 54. The method as claimed in claim 44, further comprising the following steps after the step of determining that the present sensed point is a sensed point touched by the stylus: determining a sensing point on an upper left corner of a two-by-two array within the matrix by selecting the coordinates of the sensed point touched by the stylus as a present sensed point; acquiring the capacitance variation values of the sensed points on two of the columns next to the present sensed point and determining a column of the coordinates of the sensed point on the upper left corner according to the capacitance variation values of the sensed points on the two columns next to the present sensed point; selecting the coordinates of the sensed point touched by the stylus as a present sensed point; acquiring the capacitance variation values of the sensed points on two of the rows next to the present sensed point and determining a row of the coordinates of the sensed point on the upper left corner according to the capacitance variation values of the sensed points on the two rows next to the present sensed point; and determining the two-by-two array of sensed points using the sensed point on the upper left corner.
 55. The method as claimed in claim 53, wherein the capacitance variation values of the two-by-two array of sensed points are used to determine effective coordinates of a touch object, and the effective coordinates of the touch object are determined by steps of: deducting a minimum value of the original capacitance variation values of the sensed points respectively on two columns next to the two-by-two array of sensed points and on each row of the two-by-two array of sensed points from the original capacitance variation value of each sensed point in the two-by-two array and on the same row, and obtaining a greater value of zero and the difference value as a first capacitance variation value of the sensed point in the two-by-two array; deducting the original capacitance variation value of each sensed point on both one of the rows and one of the columns next to the two-by-two array of sensed points from the original capacitance variation value of the sensed point on the same row and on adjacent one of the columns of the two-by-two array to obtain a capacitance variation difference value of the sensed point on the same row and on the adjacent column of the two-by-two array; deducting a minimum value of the two capacitance variation difference values of the sensed points respectively on the two rows next to the two-by-two array and on each column of the two-by-two array from the first capacitance variation value of each sensed point on the same column of the two-by-two array, and obtaining a greater value of zero and the difference value as an actual capacitance variation value of the sensed point in the two-by-two array; and using the actual capacitance variation values of the four sensing points in the two-by-two array to calculate the effective coordinates of the touch object by interpolation.
 56. The method as claimed in claim 54, wherein the capacitance variation values of the two-by-two array of sensed points are used to determine effective coordinates of a touch object, and the effective coordinates of the touch object are determined by steps of: deducting a minimum value of the original capacitance variation values of the sensed points respectively on two columns next to the two-by-two array of sensed points and on each row of the two-by-two array of sensed points from the original capacitance variation value of each sensed point in the two-by-two array and on the same row, and obtaining a greater value of zero and the difference value as a first capacitance variation value of the sensed point in the two-by-two array; deducting the original capacitance variation value of each sensed point on both one of the rows and one of the columns next to the two-by-two array of sensed points from the original capacitance variation value of the sensed point on the same row and on adjacent one of the columns of the two-by-two array to obtain a capacitance variation difference value of the sensed point on the same row and on the adjacent column of the two-by-two array; deducting a minimum value of the two capacitance variation difference values of the sensed points respectively on the two rows next to the two-by-two array and on each column of the two-by-two array from the first capacitance variation value of each sensed point on the same column of the two-by-two array, and obtaining a greater value of zero and the difference value as an actual capacitance variation value of the sensed point in the two-by-two array; and using the actual capacitance variation values of the four sensing points in the two-by-two array to calculate the effective coordinates of the touch object by interpolation. 